This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
Magnetization switching with high spin-orbit coupling (SOC) materials such as the giant spin Hall effect (GSHE) metals and topological insulator surface states have attracted much attention for potential memory and logic device applications. In such materials, a longitudinal charge current density (Jc) induces a transverse spin current density which if large enough can switch magnetization direction of a ferromagnet (FM). The ratio of spin current density (Js) injected into a spin load to θSHJc is given by
                                                        J              s                                                      θ                SH                            ⁢                              J                c                                              =                                    (                              1                -                                  sech                  ⁢                                                            t                      g                                                              λ                      g                                                                                  )                        ⁢                                          G                L                ′                                                                                                        σ                      g                                                              λ                      g                                                        ⁢                  tanh                  ⁢                                                            t                      g                                                              λ                      g                                                                      +                                  G                  L                  ′                                                                    ,                            (        1        )            where tg is the thickness of the GSHE layer,λg is the spin diffusion length,σg is the conductivity, andθSH is the intrinsic spin Hall angle of GSHE. G′L is the spin conductance per unit area of the spin load. Referring to FIGS. 1A and 2A, a side view and perspective view, respectively, of a prior art switching device having a spin-orbit coupling layer and a ferromagnetic layer is depicted.
The right-hand side consists of two factors each of which has a maximum value of one. Therefore, Js/(θSHJc)≤1. The first term is (1−sech tg/λg) which represents the cancellation from oppositely spin polarized back surface. This term can be maximized by using thick layers (tg>>λg). The second term is:
      G    L    ′                                σ          g                          λ          g                    ⁢      tanh      ⁢                        t          g                          λ          g                      +          G      L      ′      which is maximized if G′L>>(σg/λg).
Even under optimal conditions the maximum spin current density, Js, which is limited by θSHJc (since Js<θSHJC). As a result, the present direction of research and development in this field is based on finding materials with increased spin Hall angle θSH. However, this direction has resulted in limited success.
There is, therefore, an unmet need to find a new and novel approach to increase spin current density to effect switching polarity of ferromagnetic material with smaller charge current density.